Cooling water pump assemblies of the type to which the present invention relates include a housing, an impeller rotatably mounted in the housing on a shaft. In the assembly shown in German Application DE 2238309, the impeller is mounted on a solid shaft and a two row ball bearing rotatably supports the shaft. The raceways for the balls are machined directly into the shaft. In this assembly, the bearing is secured against the coolant circuit by means of an axial face seal and one of the sliding rings of the seal is mounted on the outer ring of the bearing. Even though this assembly is effective for the purposes intended, it is rather expensive since it is made of plurality of solid components. Further, the conductivity of the material also is a factor in temperatures generated in the bearing.